Mating is a complex motivated behavior whose expression requires the interaction of odors and gonadal steroids. These studies have relevance to understanding the regulation of complex behaviors in humans and animals because sensory and hormonal stimuli are seldom present in isolation. Instead, an organism in a natural setting is confronted with multiple signals from its internal and external environment, and the product of multimodal integration transforms the individual characteristics of these stimuli to produce a rich behavioral response. The Syrian hamster is used as a model for these studies because the male is dependent upon both odors and hormones to mate, and the basic neural circuits that mediate this behavior are known. These studies will contribute to a growing literature that hormones interact with chemosensory, visual, nutritional, and somatosensory cues to regulate reproduction. One hallmark of hormone-sensitive brain regions is the dense interconnections between steroid receptor-containing nuclei to form a hormone-responsive neural network. This network structure has profound implications for steroidal regulation of neural function. In 1986, Cottingham and Pfaff proposed that properties of the hormone-responsive neural network could include redundancy, amplification, stability and selective filtering of steroid cues to regulate reproduction, concepts which can be applied to the steroidal control of male hamster sexual behavior. The PI's laboratory recently determined that communication between odors and hormones is required for mating, and Specific Aim 1 will investigate where in the brain this is accomplished. In particular Aim 1A will use intracerebral implants of testosterone to test the hypothesis that there exist separate parallel subcircuits for transmission of odors and hormones, and that the hormonal subcircuit is functionally redundant. Aim 1B will combine intracerebral implants with unilateral olfactory bulbectomy to determine sites for integration of hormonal cues with odors. The implication is that hormones act as a selective filter for odor cues to permit mating. Specific Aim 2 will test the hypothesis that multifocal steroid action amplifies male sexual behavior using multiple implants of testosterone in the mating behavior pathway. Finally, Specific Aim 3 will investigate stability of the mating behavior circuitry through reciprocal connections of steroid-responsive subnuclei.